package com.str.stack;
public interface Stack {
  // Stack values are stacks whose elements are arbitrary objects.

// Modifiers
  public void clear();
  // Make this stack empty.

  public void push(Object val);
  // Add val as the top element on this stack.

  public Object pop();
  // Remove and return the top element from this stack, or null if this
  // stack is empty.

// Accessors
  public boolean isEmpty();
  // Return true if and only if this stack is empty.

  public int size();
  // Returns the number of elements on the stack

  public Object peek();
  // Return the element at the top of this stack, or null if this
  // stack is empty.
}
